Conventionally, in a lithography process to manufacture electronic devices (microdevices) such as semiconductor devices (integrated circuits and the like) and liquid crystal display devices, a projection exposure apparatus of a step-and-repeat method (a so-called stepper), a projection exposure apparatus of a step-and-scan method (so-called scanning stepper (also called a scanner)) and the like are mainly used.
In this type of exposure apparatus, along with finer device patterns due to higher integration of semiconductor devices, requirements for high overlay accuracy (alignment accuracy) are increasing. Therefore, requirements are increasing for higher accuracy on position measurement of substrates such as a wafer or a glass plate and the like on which a pattern is formed.
As a device for satisfying such requirements, for example, in PTL 1, an exposure apparatus is proposed equipped with a position measurement system that uses a plurality of encoder type sensors (encoder heads) which are mounted on a substrate table. In this exposure apparatus, the encoder heads measure a position of the substrate table by irradiating measurement beams on a scale which is placed facing the substrate table and receiving return beams from the scale.
However, as a premise for the exposure apparatus according to PTL 1 equipped with the position measurement system to achieve exposure with high precision, grating pitch and grating shape of the grating that the scale has are “not to vary at all” for over a long period of time. Further, even if the grid varies, there are no means for monitoring the variation except for monitoring the variation based on exposure results.
However, when considering that a permissible value of a positioning error required in a wafer stage of the current exposure apparatus is at a nm level, it is difficult to think that the grid will not vary over a long time when viewed at a nm level.
Further, transition from an age of a 300 mm wafer to an age of a 450 mm wafer is near at hand and when it comes to an exposure apparatus handling 450 mm wafers, it is considered that while the wafer stage increases in size, the permissible value of the positioning error will become tighter than the present (or around the same as the current level). Using the position measurement system according to PTL 1 described above in the exposure apparatus handling 450 mm wafers without any changes is considered to be difficult, when considering a further increase in the size of the scale (grating) that accompanies larger wafers.
A similar problem also occurs in an exposure apparatus disclosed in, for example, PTL 2 and the like that is equipped with an encoder system.